Chemosh is the god of Moab, yet Jephthah names him as the god of the Ammonites. Molech was the god of Ammon (1 Kings 11:33). Jephthah could be confused about which god is which.1 It is more likely that this is deliberate. Jephthah is not giving a historical and/or theological lecture per se. This is a political speech. Jephthah has contempt for Ammon. Earlier in his speech, he avoided even mentioning Ammon when talking about the disputed area. Now, by mentioning Chemosh instead of Molech, Jephthah is probably trying to insult the king and start the war.2
24 Will you not possess what Chemosh your god gives you to possess? And all that the LORD our God has dispossessed before us, we will possess.